Epoxy resins are used to make commercially useful articles. They are also used in a variety of adhesive compositions. Epoxy resins are noted for their low cure shrinkage and excellent adhesive properties. They are polymerized through the highly strained epoxy ring either as homo-cured thermosets or in combination of a variety of curative synergists. Several curatives can be used to cure epoxy resins. These include amines, anhydrides, phenols, thiols, cyanates, and isocyanates.
A recently described class of epoxy curatives includes phenyl esters. The phenyl esters offer a number of advantages over traditional epoxy curatives. They are, for example, much more latent than most amines, cyanates, or isocyanates. They are much more stable toward moisture exposure than cyanates, especially as compared to anhydrides and isocyanates. They do not absorb carbon dioxide from the air like many of the amines. They don't have any of the malodorous issues associated with thiols. They do not poison free radical cure (an important feature for hybrid thermoset compositions that include epoxies and free radically polymerizable monomers) like phenols. They are also considerably lower in viscosity than the corresponding phenols. The thermosets made using phenyl esters are also generally more hydrophobic than those containing other epoxy curatives. The cure of a phenyl ester with an epoxy resin results in a continuous network of ether linkages with pendant secondary ester linkages. The polyether backbone of the final thermoset is considered to provide superior hydrolytic resistance. However, the epoxy-phenyl ester compositions previously described in the literature tend to be brittle.